THERMOCHEMISTRY OF GASEOUS ZRF, ZRF2, AND ZRF3

Several gaseous reaction equilibria involving the lower-valent Zr-F sp ecies were studied by mass spectrometry over parts of the range 1400 - 2400 K, and the derived reaction thermodynamics were used to evaluate the bond dissociation energies, BDE, and standard enthalpies of forma tion, Delta(f)H(298)(o), of the gaseous species ZrF, ZrF2, and ZrF3. E mphasis was placed on correlation of the second and third law results as an aid in selecting the proper thermal functions. BDE values at 298 KI measured by reference to the molecule BaF, were found to be D(Zr-F )=149.9 +/-2.5;D(FZr-F)=161.2+/-2.5;D(F2Zr-F)=149.6+/-4.5; and D(F3Zr- F)=157.9+/-2.5 kcal mol(-1). Corresponding values of Delta(f)H(298)(o) for the gaseous species were calculated to be ZrF, 12.3+/-2.8;ZrF2,-1 29.9+/-3.7 and ZrF3,-260.5+/-2.8 kcal mol(-1). The results are discuss ed in terms of other information in the literature. When all results a re evaluated with consistent thermal functions and auxiliary data, the re is reasonable agreement among derived thermochemical values. (C) 19 97 American Institute of Physics.